Planning for a Shorter Rainy Season and More Frequent Extreme Storms in California
Nov 15, 2020 at 8:00am
California’s hydrologic future is muddled by a fundamental uncertainty: will the state get wetter or drier? Climate models disagree on this question, but provide insights on other important water management questions.
The wetter or drier question has been studied often in government reports (DWR CCTAG, 2015; U.S. Bureau of Reclamation, 2016) and a variety of academic studies (Connell-Buck et al., 2011; Dogan et al., 2019; Medellín-Azuara et al., 2008). Forecasts for California mean annual precipitation commonly range from at least 20% wetter to 20% drier on average.
This focus on the uncertainty of future mean annual precipitation has unnecessarily deterred investment in adaptive management of water resources (Persad et al., 2020). While there is little model agreement on change in mean annual precipitation, there is much more model agreement on other hydroclimate metrics relevant to water resources management, including:
- snowpack declines
- increased fraction of precipitation on extreme rainfall days
- a shorter, sharper rainy season
- increased ET
- higher frequency of extremely wet and extremely dry years, and
- higher incidence of “whiplash” years where an extreme dry year follows an extreme wet year or vice versa.